1. Field of the Invention
The invention relates to an electronic device, and more particularly to a capacitor with a floating metal ring.
2. Description of the Related Art
Capacitors are essential passive elements in integrated circuits. In integrated circuits, differential signals on two electrodes of a capacitor are easily affected by nearby routed conducting lines. FIG. 1 shows a capacitor of symmetric metal-oxide-metal (MOM) structure. Electrodes E10 and E11 and an oxide layer therebetween form a capacitor CP1. If there is a conducting line L10 near the capacitor CP1, parasitic capacitors are formed between the conducting line L10 and the electrodes E10 and E11. FIG. 2 shows an equivalent circuit of the MOM structure and the conducting line L10. Referring to FIGS. 1 and 2, C10 represents the parasitic capacitor between the conducting line L10 and the electrode E10, and C11 represents the parasitic capacitor between the conducting line L10 and the electrode E11. Noise on the conducting line L10 directly affects the differential signals on the electrodes E10 and E11. Moreover, since the electrode E11 is farther away than the electrode E10 from the conducting line, the parasitic capacitor C11 is smaller than the parasitic capacitor C10, so that, the differential signals on the electrodes E10 and E11 suffer unequal effects from the conducting line L10.